Dinuclear EGTA-copper(II) chelates with imidazole as auxiliary ligand

By reaction of Cu2CO3(OH)2 and H4EGTA with or without imidazole, the compounds [Cu2(EGTA)(H2O)2] · 2H2O (1), [Cu2(EGTA)(Him)2]n (2) and [Cu2(EGTA)(Him)4] · 4H2O (3) have been prepared. The EGTA acts in a μ2-bridging mode, with each half being tripodal-tetradentate in mer-NO2 + O(ether, apical) or NO + O(carboxy, apical) + O(ether, apical) conformation for compounds 1 and 2 or 3 and [Cu2(EGTA)(en)2] · 4H2O (4), respectively, as expected from the number of N donor atoms (0 and 1 or 2) supplied by the auxiliary ligands. The Cu–O(ether) bond length increases in the series 1 < 2 < 3 < 4, mainly influenced by the coordination number (5 or 6) of the copper(II) atom, the influence of the Jahn–Teller effect on it, giving from 4 + 1 to 4 + 1 + 1 surroundings, and the number of N atoms (1 to 3) among the four closest donor of the Cu(II) atom.